families, communities, and jobs – of having large numbers of people
with drug addiction.
Because the success of different control strategies can vary
between the three stages of a drug epidemic, it’s crucial to know what
stage we’re currently in. In theory, it should be possible to work this
out by estimating the annual numbers of new users, existing users,
and heavy users. But the complexity of the opioid crisis – with its mix
of prescription and illegal use, makes it very difficult to pick these
things apart. There are some useful data sources – such as visits to
emergency rooms and results of post-arrest drug tests – but this
information has become harder to get hold of in recent years. We
can’t draw a neat graph showing the different stages of drug use like
we can for the Yambuku Ebola outbreak, because the data simply
aren’t available. It’s a common problem in outbreak analysis: things
that aren’t reported are by definition tough to analyse.
I of a disease outbreak, there are generally two
main aims: to understand transmission and to control it. These goals
are closely linked. If we improve our understanding of how something
is spreading, we can come up with more effective control measures.
We may be able to target interventions at high-risk groups, or identify
other weak links in the chain of transmission.
The relationship works the other way too: control measures can
influence our understanding of transmission. For diseases, as with
drug use and gun violence, health centres often act as our windows
onto the outbreak. It means that if health systems are weakened or
overburdened, it can affect the quality of data coming in. During the
Ebola epidemic in Liberia in August 2014, one dataset we were
working with suggested that the number of new cases was leveling
off in the capital Monrovia. At first this seemed like good news, but
then we realised what was actually happening. The dataset was
coming from a treatment unit that had reached capacity. The case
reports hadn’t peaked because the outbreak was slowing down;
they’d stopped because the unit couldn’t admit any more patients.
The interaction between understanding and control is also
important in the world of crime and violence. If authorities want to